The present invention relates to a print method and apparatus for printing an image on a printing medium using a print means.
In recent years, color printers using various print schemes have been developed as color image print equipment. Of these printers, serial ink-jet printers that print in units of lines (bands) are popularly used owing to their merits, i.e., since they are inexpensive, can print high-quality images on a large number of kinds of print media, can be easily made compact, and so on.
Such serial printer forms a print image by developing print information for one scan into image data to store the data in a memory, and driving the print elements of a printhead on the basis of the developed image data while scanning the printhead with respect to a printing medium. Among such serial printer apparatuses, a color printer apparatus that prints a color image using color inks is known, and as its printhead, a head prepared by vertically arranging print element groups for printing yellow, magenta, cyan, and black image data in a direction perpendicular to the scanning direction of the printhead is popularly used. In the printhead with this arrangement, the print element groups corresponding to the individual colors are arranged to be separated by given intervals to produce a delay time from when the print scan using one color print element group is complete for the printing medium until the print scan of print data of the next color is started, thereby eliminating color smearing. Also, a decrease in print speed caused by the delay time is prevented. In this manner, color nonuniformity, smearing, and the like, which are produced between adjacent different color dots on the printing medium, can be eliminated, and a color output with high image quality can be realized.
In recent years, many printer apparatuses perform binarization processing for image data including multi-valued information per pixel like a picture image and output the processed data. When such multi-valued data is converted into binary data, the size (dot area) of one pixel printed and its lightness determine the graininess of the image. More specifically, it is generally known that the graininess increases as the area (dot shape) of one pixel printed is larger, and as the lightness of the pixel is lower (its density is higher). As a technique for reducing the graininess in a printed image, a technique for reducing the area of each pixel (dot) to be printed to increase the resolution of the printed image has been proposed.
In order to increase the resolution of print data in the conventional color printer apparatus, the storage capacity of a memory means (print buffer) for storing image data must also be increased. For example, when one pixel is printed as 4-gradation data, the pixel data requires 3 bits. More specifically, a storage capacity three times that for 1-bit pixel data is required. Normally, the print buffer comprises a RAM (random access memory). Since the cost of such RAM is roughly determined in proportion to its memory capacity, an increase in storage capacity of the memory raises the cost of the apparatus.